According to this invention, an improved large pore volume zirconia-silica catalyst support useful in olefin polymerization catalysts is prepared by reacting a particular zirconium compound with an alkali metal silicate to produce a hydrocogel, aging the hydrocogel, washing the hydrocogel with an aqueous washing agent, removing water from the resulting washed hydrocogel to produce a xerocogel either by azeotropic distillation or by leaching with a water miscible solvent, and calcining the resulting xerocogel.
A further feature of the invention is a method of polymerizing olefins comprising contacting the olefins with a catalyst comprising the above support and a chromium compound associated with it under polymerizing conditions.
The most pertinent prior art of which we are aware are the following:
U.S. Pat. No. 2,289,919 discloses purified silica hydrogel (free of sodium ion) suspended in a zirconium salt solution (aqueous zirconyl chloride). Aqueous ammonium hydroxide is then added in order to precipitate zirconia onto the hydrogel (not coprecipitated). The zirconia-silica mixture is washed, dried at 300.degree. F., and calcined.
U.S. Pat. No. 2,444,913 discloses a method of preparing plural oxide catalysts containing zirconia and silica which comprises preparing a solution containing silica and zirconia by mixing an alkali metal silicate solution with an alkali metal zirconium carbonate solution and coprecipitating the silica and zirconia in said solution by the addition of an acid to a pH of about 6.5. The hydrogel is dried at 200.degree.-210.degree. F. and calcined at 1400.degree. F. in an air-stream.
U.S. Pat. No. 3,950,316 discloses a method of preparing a silica-titania catalyst support comprising mixing a water soluble titanium compound (potassium titanium oxalate, K.sub.2 TiO(C.sub.2 O.sub.4).sub.2.2H.sub.2 O or ammonium titanium oxalate, (NH.sub.4).sub.2 TiO(C.sub.2 O.sub.4).sub.2.H.sub.2 O with an alkali metal silicate solution, said titanium compound being nonreactive with the silicate, adding an acidic material to the silicate containing the titanium compound to form a hydrogel, aging the hydrogel for more than one hour, washing the aged hydrogel with either an ammonium salt solution or a dilute acid to produce an alkali-free hydrogel, forming a mixture comprising said washed hydrogel and a normally liquid oxygen-containing water soluble organic azeotrope-forming compound, separating the organic compound with water to form a xerogel. In the present invention, in contrast, the zirconium oxalate is reactive with the alkali metal silicate. For example, ammonia gas is liberated when ammonium zirconium oxalate is mixed with sodium silicate solution.
U.S. Pat. No. 3,862,104 is similar to the above U.S. Pat. No. 3,950,316 except potassium titanate oxalate in aqueous solution with sodium silicate is added to an ammonium sulfate solution.
U.S. Pat. No. 3,801,705 discloses a method for providing a silica xerogel having a narrow pore diameter distribution within the range 300-600.ANG., surface area within the range 200-500 m.sup.2 /g, and a large pore volume between 2-3.5 cc/g.
None of the above discloses the claimed invention.